1. Field of the Invention
Exemplary embodiments of the present invention relate to an electric vehicle or hybrid vehicle having no torque converter; and, particularly, to a vibration reduction algorithm for a vehicle having no torque converter, in which optimized feedforward logic based on a step torque or ramp torque, which is provided separately depending on an acceleration/deceleration state of the vehicle, is performed by a feedforward control function, thereby significantly reducing a time required for heuristic calibration and significantly improving launch acceleration performance.
2. Description of Related Art
In general, when an automatic transmission is implemented in an electric or hybrid vehicle, the automatic transmission does not use a torque converter like is required in a gasoline or diesel vehicle. Typically, the torque converter may serve as a damping element between an engine and a driving system (e.g., transmission and power transfer system) to reduce vibrations transmitted from the engine, in addition to converting torque from the engine to the transmission. Automatic transmissions in an electric or hybrid vehicle, however, cannot implement a damping operation using a torque converter. Therefore, in these types of vehicles, vibrations from the driving system (e.g., transmission and power transfer system), caused by a torque source of an engine or motor, are not reduced properly. Furthermore, vibrations from the driving system caused by an external vibration source are not reduced properly, either.
Accordingly, when a vibration reduction operation that takes into consideration the lack of a damping element is not implemented between the torque source (e.g., engine and motor) and the driving system (e.g., transmission and power transfer system) in an electric or hybrid vehicle, the driving and riding quality thereof are inevitably decreased. As a result, the merchantability of the vehicle also decreases.
The lack of a damping element may be overcome by executing hardware or an algorithm in therein. However, since using hardware is typically quite costly, algorithmic corrections are usually preferred by most automotive manufactures. However, when hybrid and electric vehicles are driven by motor power, the motor is not typically driven at a following motor velocity (i.e., theoretical motor velocity) where vibrations based on a motor applied torque do not occur, but instead are driven at an actual motor velocity where vibrations based on a motor applied torque do occur. Accordingly, vibration reduction measures are inevitably needed.
Examples of the vibration reduction measures may include a vibration reduction control algorithm through feedforward control logic.
The vibration reduction control algorithm may be implemented according to control logic in which a feedforward control function CFF(s) outputs a motor command torque, a feedback control function CFB(s) calculates a vibration reduction torque for suppressing speed vibration extracted as motor sensor speed (i.e., measured by a sensor installed in the motor) and motor model speed (i.e., estimated through modeling), and a driving system transfer function G(s) outputs a final motor command torque obtained by summing the motor command torque and the vibration reduction torque.
That is, the motor command torque transferred to the driving system transfer function G(s) may be calculated, feedback information may be used to calculate the vibration reduction torque, the motor command torque and the vibration reduction torque may be summated and converted into the final motor command torque, and the final motor command torque may be continuously adjusted according to the feedback information. Therefore, when the vibration reduction control algorithm is applied to a hybrid or electric vehicle driven by motor power, it is possible to reduce vibrations caused by the actual motor velocity which do not coincide with a following motor velocity, thereby improving the driving and riding qualities of the vehicle.
FIG. 3 as relevant prior art illustrates an example of a linear system having a feedforward control function which is performed based on the step torque and the ramp torque which are provided as a feedforward value. Referring to FIG. 3, the linear system includes a feedforward control function 10 GFF(s), a feedback control function 30 CFB(s), and a driving system transfer function 20 G(s). The feedforward control function 10 GFF(s) is configured to receive one torque profile between a step torque Ts and a ramp torque Tr according to an acceleration/deceleration state of the vehicle, and output a motor command torque. The feedback control function 30 CFB(s) is configured to provide feedback information as information for calibrating the motor command torque through heuristic calibration. The driving system transfer function 20 G(s) is configured to receive the motor command torque which is continuously calibrated. The torque outputted from the driving system transfer function 20 G(s) is converted into the actual motor velocity V.
However, since the above-described algorithm is implemented according to the feedback control logic, the algorithm inevitably has fundamental limitations because it must rely on calibration characteristics associated with the vehicle without a mathematical analysis on unique characteristics each vehicle.
Typically, the calibration characteristics of the vehicle are performed according to a heuristic algorithm. The heuristic algorithm refers to an algorithm that searches for a solution which is practically satisfactory in consideration of limited information and time constraints, without searching for the most ideal solution. Due to such characteristics, the algorithm relying on the heuristic calibration for characteristics of the vehicle is difficult to systemically design. In particular, since the heuristic calibration must be performed differently depending on vehicle types, the time consumption inevitably increases.
Therefore, since the above-described algorithm is not sufficient to effectively realize vibration reduction, the algorithm has at least one impractical limitation which should be addressed. Furthermore, due to this limitation, the launch acceleration performance of the vehicle is degraded as a result.